Recent surveys indicate that between 10 and 20 percent of homes in the United States have indoor radon levels that exceed EPA's guideline level for remedial action. It has been estimated that indoor radon pollution accounts for 5,000 to 20,000 lung cancer deaths each year. This estimates is extrapolated from studies of miners with very high radon exposures; results which may not be generalizable to the population at large. Cigarette smoking is the overwhelming risk factor for lung cancer and there is evidence to suggest that effects from radon may be greater in smokers. However, the nature of the possible interaction between radon smoking has not been adequately quantified. Furthermore, while most studies have focused on lung cancer risk, the possibility of broader effects of radon exposure cannot be ruled out. Accordingly, the relationship between cumulative residential exposure to radon and cancer risk will be explored in Connecticut, in a population-based study of approximately 400 nonsmokers and 600 smokers with lung cancer and a similar number of matched comparison subjects without lung cancer chosen by random population screening. Incident cancer cases identified through a statwide cancer registry will be collected over a 3 year period. Detailed residential histories will be obtained and radon measurements will be made in past homes in order to estimate cumulative radon exposure for each subject. The joint and interactive effects of radon and cigarette smoke exposure on lung cancer risk will be evaluated. In a preliminary companion study, cumulative radon and background gamma radiation exposure will also be determined for approximately 125 childhood cancer cases and 250 healthy controls.